As known in the art, a color liquid crystal display (LCD) panel 1 has a two-dimensional array of pixels 10, as shown in FIG. 1. Each of the pixels comprises a plurality of sub-pixels, usually in three primary colors of red (R), green (G) and blue (B). These RGB color components can be achieved by using respective color filters. FIG. 2a illustrates a plan view of the pixel structure in a conventional transmissive LCD panel. As shown in FIG. 2a, a pixel 10 can be divided into three sub-pixels 12R, 12G and 12B. Three data lines 21, 22 and 23 are used to separately provide data line signals to sub-pixels 12R, 12G and 12B. The data line 24 is used to provide data line signals to the neighboring pixel column. Also, a single gate line 31 is used to activate the pixel 10. The gate line 32 is used to provide a gate line to the neighboring pixel row. It should be noted that the color sub-pixels 12R, 12G and 12B can also be arranged in a different orientation. As shown in FIG. 2b, a single data line 21 is used to provide data line signals to all three color sub-pixels 12R, 12G and 12B, and three gate lines 31, 32 and 33 are used to separately activate the color sub-pixels 12R, 12G and 12B. The data line 22 is used for providing data line signals to the neighboring pixel column and the gate line 34 is used for activating the neighboring pixel row. The pixel 10 as shown in FIG. 2a is also known as a tri-gate pixel.
In a vertical alignment (VA) liquid crystal display (LCD), the liquid crystal molecules in the display are aligned substantially along a vertical axis that is perpendicular to the substrates in the absence of an electric field. When the voltage above a certain value is applied to electrodes formed on the substrates, the molecules are aligned in a different direction, away from the vertical axis. VA-LCD has the advantages of a wider viewing angle and a higher contrast ratio than the conventional LCD.
A VA-LCD can be further improved by introducing cutouts or protrusions in each pixel so as to change the orientations of the liquid crystals into different domains. This type of VA-LCD is known as multi-domain VA-LCD or MVA-LCD. MVA-LCD further widens the viewing angle. It is known that, in an MVA-LCD display, the lateral visibility is far inferior than the frontal visibility.
In a patterned vertical alignment liquid crystal display (PVA-LCD), the lateral visibility can be improved by dividing a pixel into two sub-pixels, wherein the applied voltage in one sub-pixel is shared by the other through capacitive coupling, such that the voltages in the two sub-pixels are different. Thus, each pixel has two electrodes, as shown in the schematic presentation of FIG. 3. As shown in FIG. 3, a liquid crystal display has a first substrate, a second substrate and a liquid crystal layer disposed between the first and second substrates. In each sub-pixel 12, a common electrode, connected to a common voltage Vcom, is provided on one substrate, and two separate electrodes are located on the other substrate to provide two different vertical electric fields, at least in a time period after the pixel 12 is activated by a gate line signal. Typically, the pixel 12 is associated with a number of capacitors, such as the charge capacitance of the liquid crystal layer in the sub-pixel and various charge storage capacitors fabricated in the sub-pixels in order to maintain the voltage potential between the upper and lower electrodes after the gate line signal has passed. When the gate line signal is “on”, it drives a TFT, for example, to charge up these capacitors so that the voltage level on the electrode in each sub-pixel is substantially equal to the signal on the data line, at least before the gate line signal has passed. In a PVA-LCD, the voltage potentials in the two sub-pixels after the gate line signal has passed are different. In prior art, this is achieved by using one or more capacitors for charge sharing.